This invention relates to an electronically scanned antenna, and more particularly to an electronically controlled antenna in which the radiation level, radiation angle, etc. of a plurality of beams in two radiation planes, orthogonal with each other, are electronically controlled.
In a typical prior art electronically scanned antenna, the antenna array is mounted on a mechanically rotating pedestal so as to scan the antenna beam in a horizontal plane at a constant speed while the beam is electronically scanned in an elevation plane. Consequently, when such an antenna is used in a radar system, the acquisition percentage of data obtained from a target is a constant value determined by the rotational speed of the antenna, and the number of hits is also a substantially constant value determined by the rotational speed therefore, it has been difficult to adaptively increase the percentage of data obtainable from the target when the antenna turns or to adaptively increase the number of hits in accordance with the nature of the input signal.
To solve these problems, an antenna has been proposed wherein the beam is electronically scanned in a solid angle of predetermined elevation angle and azimuth. Such an antenna, however, requires a square of the number of such component elements as phase shifters or the like when compared with an antenna in which the beam is electronically scanned in the elevation angle alone, whereby the construction of the antenna becomes complicated and expensive.
Another example of the prior art antenna is shown in FIG. 1 in which a plurality of antenna radiation units are mounted on a single rotary pedestal. More particularly, the antenna comprises radiation apertures 1 and 5, vertical feed circuits 2 and 6 respectively feeding the radiation apertures 1 and 5, input terminals 3 and 7 to the feed circuits 2 and 6, a high power transfer device 9 with an input terminal 10 and a rotary pedestal 11. The radiation apertures 1 and 5 form radiation beams 4 and 8, respectively.
In the antenna shown in FIG. 1, the power applied to the input terminal 10 through the rotary pedestal 11 is selectively supplied to the input terminal 3 or 7 of the feed circuit 2 or 6 by the power transfer device 9 to form antenna beam 4 or 8. In operation, subsequent to searching and measuring a specific target with the antenna beam 4, when the antenna beam 8 catches the target as the pedestal 11 rotates, the power transfer device 9 transfers the energy to the feed circuit 6 so as to search and measure the object with the antenna beam 8, thereby doubling the acquisition percentage of data regarding the object.
This type of antenna, however, requires two independent antenna radiation units so that the antenna system becomes large and expensive. Moreover, the capacity of the power transfer device should be large because it is necessary to transfer the total power of the radar.
In a prior art pulse radar system in which the position of a target is searched by receiving pulses reflected by such a flying target as an airplane and then processing the resulting position information, for the purpose of increasing the number of pulse hits (hereinafter merely termed the number of hits) obtainable from the target or acquisition percentage of data obtained under specific conditions, the radiation angle of an antenna array is electronically controlled according to a predetermined pattern in the case of a stationary antenna. But in the case of an antenna mounted on a rotary pedestal rotatable in a horizontal plane, the radiation angle of an antenna array is electronically controlled according to a predetermined pattern corresponding to the rotational movement of the antenna. In the cases of the stationary electronically controlled antenna and of the electronically controlled antenna mounted on the rotary pedestal, the number of component elements including phase shifters, etc., utilized to control the multi-radiation beams increases greatly so that the antenna becomes complicated and the cost of installation and operation increases. Moreover, the reliability of operation decreases. Where the electronically controlled antenna is mounted on the rotary pedestal, it is necessary not only to install a number of antenna arrays but also to install a high power transfer device for the feed system of the plurality of antenna arrays. This not only complicates the construction of the antenna and increases the cost of installation and operation but also decreases the reliability.